(1) Field of the Invention
The present invention relates to a pressure-compensation device, and more particularly to an interior pressure-compensation device for cartridges that can stabilize the internal backpressure of the cartridge for ink jet printers.
(2) Description of the Prior Art
In the computer industry, an ink jet printer, one of the well-known computer peripheral devices, performs printing jobs by providing ink drops from a cartridge through a print head onto a piece of paper or other recording media.
In the art, a well-designed cartridge for ink-jet printer should comply with the following two requirements:
1. While the cartridge is at an idle state, the internal pressure Pi of cartridge should be less than the external atmosphere pressure Po to prevent the cartridge from ink leakage through the print head.
2. While the cartridge is at a printing state, an additional pressure needs to be provided to increase the internal pressure Pi of the cartridge to overcome the external atmosphere pressure Po so that the ink inside the cartridge is able to drop out through the print head and accomplish the intended printing job.
To satisfy the aforesaid first requirement, a resort in the art is to add a backpressure Pb into the cartridge to provide a minus pressure for reducing the internal pressure Pi. By maintaining the internal pressure Pi of the cartridge to be less than the external atmosphere pressure Po during cartridge""s idle state, the possible ink leakage from the print head can be prevented.
On the other hand, to satisfy the aforesaid second requirement, a resolution in the art is to utilize a specific print head of thermal bubble type or piezoelectric pressure wave type, which is able to generate a proper print pressure P inside the cartridge during printing. When the printing pressure P is greater than the backpressure Pb, the internal pressure of cartridge Pi reaches a pressure level higher than the external atmosphere pressure Po so that the cartridge allows ink to drop out through the print head to perform the intended printing function. The art of print head is not within the scope of the present invention, therefore, no more efforts thereinafter will be devoted to it.
It is understood that the atmosphere pressure Po varies along with the ambient. For example, the atmosphere pressure Po in a flying airplane or at a location of higher elevation is always smaller than the atmosphere pressure on the ground, so it is not unusual at some locations that the internal pressure Pi of cartridge will be greater than the atmosphere pressure Po, which causes ink to drop out from the cartridge through the print head even when no printing job is at work.
In addition, the backpressure Pb inside the cartridge increases along with the gradual exhaustion of the ink. Therefore, when the backpressure Pb is greater than the print pressure P of print head, the printing job is unable to proceed and the cartridge needs to be replaced even though there is still some ink left in the cartridge.
To resolve the aforesaid disadvantages of the cartridge, a pressure-sensitive accumulator for ink-jet pens disclosed in a U.S. Pat. No. 5,409,134 introduces a device for adjusting backpressure Pb inside the cartridge by maintaining the internal pressure Pi lower than the atmosphere pressure Po within a proper range, so the aforesaid ink leakage and residual ink problems may be successfully avoided. The technique provided in the U.S. patent will be briefly stated as follows.
Referring to FIG. 1A and FIG. 1B, two states of a traditional cartridge 1 with the pressure-sensitive accumulator 10 of U.S. Pat. No. 5,409,134 are shown, respectively. The pressure-sensitive accumulator 10 includes a spring 12 and an accumulator bag 14. The spring 12 further includes a fitment 121, anchoring the spring 12 to a top portion inside the cartridge 1, and two spring legs 122, positioned at opposing ends of the fitment 121. The accumulator bag 14, an inflatable bag structure, further includes an air duct 143, a ventilating means to the atmosphere, and two opposing sides 141 and 142, connected at both ends to form a bag structure. The outer side 141 is attached to the spring leg 122.
While completing the cartridge 1, instead of completely filled with ink, a small interior space inside of the cartridge is left to allow exterior air to flow into the accumulator bag 14 through the air duct 143. Upon the air expanding the accumulator bag 14 inside the cartridge 1, the spring legs 122 of the spring 12 will be bent to a shape as shown in FIG. 1B. The resilience provided by the deformed spring legs 122 will restrain the expansion of the accumulator bag 14 and induce a backpressure Pb to the interior of the cartridge 1. The induced backpressure Pb will then contribute to the internal pressure Pi to be less than the external atmosphere pressure Po. The air duct 143 connects the external atmosphere with the interior of the accumulator bag 14, keeping the internal pressure Pi of the cartridge 1 less than the external atmosphere pressure Po, so no ink leakage occurs even when the cartridge 1 is brought to a higher elevation or inside a flying airplane.
As the ink inside the cartridge 1 runs off gradually, the accumulator bag 14 of the pressure-sensitive accumulator 10 is increasingly inflated, as shown in FIG. 1B, which deforms the spring legs 122 further to produce more backpressure Pb in the interior of the cartridge 1 to prevent the possible ink leakage.
Nevertheless, the aforesaid pressure-sensitive accumulator 10 does exist some practical disadvantages related to the spring legs 122. Since the backpressure Pb increases along with the deformation of the spring legs 122, as the printing job proceeds, ink continuously drops through the print head from the cartridge 1 until the backpressure Pb inside the cartridge 1 is greater than the print pressure provided by the print head (not shown in figures). The dropping of ink is then ceased even when there is still some ink left in the cartridge 1. It is clear that this disadvantage will lead to the waste of ink.
Accordingly, it is a primary object of the present invention to provide a pressure-compensation device that can adjust the backpressure inside the cartridge within a proper range to assure the normal operation of printing and prevent from possible ink leakage.
It is another object of the present invention to provide a pressure-compensation device for a cartridge, which can stabilize the backpressure inside the cartridge to assure that the printing proceeds smoothly till ink inside the cartridge runs out completely.
The pressure-compensation device of the present invention is designed for the cartridge of ink-jet printer. The cartridge is a sealed container whose internal space accommodates a substantial amount of ink. The pressure-compensation device includes an accumulator bag, a resilient element, and a motion element. A tension spring will be used as an embodiment for the resilient element in the following description.
Inside of the cartridge, formed as a sealed space, is used for storing ink. The accumulator bag is installed inside of the cartridge at a position on top of the stored ink, and the bag interior communicates with the external atmosphere through an air duct. While the ink inside the cartridge is gradually running off, external air is led into the interior of the accumulator bag through the air duct so as to inflate and thus extend the accumulator bag downwards.
The tension spring includes a first end engaged with the bottom end of the accumulator bag, and a second end engaged with the motion element, in which the tension spring is always kept at a tension state. The resilience provided by the elongated tension spring acts against the inflation of the accumulator bag so as to induce a proper backpressure inside the cartridge, in which the backpressure assures the interior pressure of the cartridge to be less than the external atmosphere pressure, thus, to prevent from possible ink leakage.
As the ink inside the cartridge gradually runs off along with the progression of printing work, the external air automatically feeds through the air duct and inflates the accumulator bag. Once the inflating force of the accumulator bag is able to overcome the maximum static friction of the motion element, it can move the tension spring and motion element downwards and thus maintain the backpressure inside the cartridge within a proper range, so that the ink leakage due to the lack of backpressure or the failure to drop ink due to over-backpressure can be avoided.
The motion element of the first embodiment in accordance with the present invention is designed similarly to a piston structure, which includes a piston bar and a penetration hole at the cartridge for the piston bar to penetrate therethrough. The piston bar, connected with the second end of the tension spring, must overcome the maximum static friction against the penetration hole before sliding can be triggered in between. The accumulator bag is gradually inflated along with the consumption of the ink inside the cartridge. Once the inflating force of the accumulator bag is able to overcome the maximum static friction between the piston bar and the penetration hole, the bottom portion of the accumulator bag can drag the tension spring and the motion element downwards to prevent from possible instability of the backpressure inside the cartridge caused by over tensioning the tension spring. Upon such an arrangement, the present invention is then able to prevent from the possible ink leakage during the idle state and to assure the success of ink dropping through the print head during printing.
The design of the motion element of the second embodiment in accordance with the present invention is similar to that of the first embodiment, whereof the major difference is that the tension spring and the motion element of the second embodiment are located inside the accumulator bag and are used to move with the bottom of the accumulator bag so as to maintain a stable backpressure inside the cartridge while the ink is gradually running off.
The motion element of the third embodiment in accordance with the present invention is formed by a plurality of pulley sets, preferably by a pair of parallel pulley set. Each of the pulley sets includes two fixed pulleys and a rope, whereof the two fixed pulleys are located separately at the top and at the bottom inside of the cartridge and the rope is wound around the two fixed pulleys. At least one fixed pulley of the pulley sets includes a torque limiter for providing a minimum forcing limit to rotate the pulley sets.
Both ropes of the aforesaid two pulley sets are connected with the second end of the tension spring that, as stated above, is kept at a tension state. The resilience of the tension spring restrains the inflation of the accumulator bag so as to maintain a proper backpressure inside the cartridge. As the accumulator bag is gradually inflated along with the consumption of the ink, the accumulator bag may move the tension spring and the rope downwards to maintain the backpressure inside the cartridge within a proper range to prevent from the ink leakage due to the lack of backpressure or the fail of ink dropping due to over-backpressure.
The design of the motion element of the fourth embodiment in accordance with the present invention is similar to that of the third embodiment, whereof the major difference is that the tension spring of the fourth embodiment is located at the bottom of the cartridge and is kept at a tension state. The resilience provided by the tension spring restrains the inflation of the accumulator bag so as to maintain a proper backpressure inside the cartridge. As gradual consumption of the ink, the motion element and the tension spring are moved by the inflated accumulator bag to maintain the deformation of the tension spring at a stable state and thus prevent the instability of backpressure inside the cartridge, by which possible ink leakage due to the lack of backpressure or the fail of ink dropping due to over-backpressure can be avoided.
As the accumulator bag is gradually inflated along with the consumption of the ink, when the inflation overcomes the torque limit of the toque limiter, the accumulator bag can move the tension spring and the rope downwards to maintain the backpressure inside the cartridge within a proper range, so that disadvantages of the ink leakage or the fail of ink dropping can be waived.